A non-aqueous electrolyte battery in which charge/discharge is performed by transfer of a lithium ion between a negative electrode and a positive electrode is actively studied and developed as a high energy density battery.
A non-aqueous electrolyte battery using a lithium transition metal composite oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material has already been commercially available.
In recent years, a non-aqueous electrolyte battery using a lithium titanium composite oxide of which a lithium absorption/desorption potential based on a lithium electrode is high, namely about 1.55 V, as compared to the carbonaceous material, has been put into practical use. Hereinafter, “based on lithium electrode” is sometimes represented by vs. Li/Li+. The lithium titanium composite oxide is excellent in cycle property since a volumetric change caused by charge-discharge is small. Further, since the lithium titanium oxide is free from precipitation of lithium metal in the negative electrode during lithium absorption/desorption, large current charging is enabled.
In the lithium transition metal composite oxide use as the positive electrode active material, a transition metal such as Co, Mn, and Ni is generally used. Examples of a typical, lithium transition metal composite oxide include lithium cobalt oxide (LiCoO2). A theoretical capacity of the composite oxide is 274 mAh/g. However, an actual battery in which a positive electrode potential is 4.2 to 4.3 V vs. Li/Li+ is used only about 60% of the theoretical capacity. Therefore, if a charging potential is enabled to higher, use of 70% or more of the theoretical capacity as a positive electrode capacity is enabled, and a high capacity and a high energy density of the battery are realized.
For example, JP-A 2005-085635 (KOKAI) discloses a non-aqueous electrolyte secondary battery which is provided with a positive electrode containing lithium cobalt oxide as a positive electrode active material, a negative electrode containing a graphite material, and an electrolyte solution containing ethylene carbonate as a solvent and is charged with a charge cutoff voltage of 4.3 V or more. In the non-aqueous electrolyte secondary battery, it is capable of attaining an excellent cycle property by using the lithium cobalt oxide as the positive electrode active material, the lithium cobalt oxide being produced by depositing a zirconium compound on the surfaces of a particle thereof.
JP-A 2005-317499 (KOKAI) discloses a non-aqueous electrolyte secondary battery which is capable of attaining a charge cutoff voltage of 4.3 V or more without causing deterioration of a charge-discharge cycle property and thermal stability by using a positive electrode active material which is mixed a lithium transition metal composite oxide A and a lithium transition metal composite oxide B. The composite oxide B is obtained by containing at least both Zr and Mg into LiCoO2. The composite oxide B has a layered structure and containing at least both Mn and Ni as transition metals.